Productivity, carcass composition, waste output and sensory characteristics of large barramundi Lates calcarifer fed high-nutrient density diets

This study was undertaken to examine the potential for using high-nutrient density diets with large barramundi (Lates calcarifer). Four dietary treatments, including a bait-fish treatment and three extruded formulations (H: 43% protein, 24 MJ/kg; M: 47% protein, 23 MJ/kg; L: 54% protein, 20 MJ/kg) were fed to fish with an initial weight of 1187.8 ± 9.3 g/fish. After a 12-week period, there were no significant differences in weight gain among any of the treatments with fish growing to a mean weight of 2170.8 ± 25.5 g/fish across all treatments. Growth responded positively to protein intake, but was more strongly defined by energy intake traits. There was a strong negative relationship between diet energy density and feed intake, with a reduced consumption with increasing energy density. There were significant improvements in FCR with increased energy density of the feeds. An exception to this was the bait-fish, which on a dry matter basis had an energy density of 27.3 MJ/kg, which when fed to barramundi had a dry basis FCR of 1.24: 1, worse than that of the H diet (1.12: 1). Both protein and energy utilisation efficiency were best with the H diet. Carcass lipid contents were highest in the bait-fish fed barramundi (141 g/kg) and lowest in the L diet fed barramundi (81 g/kg). Protein content of the carcass was unaffected by diet. The dress out (HOGG) yield was highest for fish fed the L diet and lowest for fish fed the bait-fish. Both the H and M diets produced HOGG yields similar to each other (∼ 86.5%). A sensory assessment of fillets from fish from each treatment showed several differences between the bait-fish fed and extruded diet fed barramundi, and a few differences among the extruded diets. A mass-balance assessment of the discharge effects associated with each diet shows considerable advantages in reducing the amount of wastes produced with the use of extruded diets. This work has demonstrated that for large barramundi there are significant advantages to using higher energy density diets than are currently used by industry.